A permanent magnet type of synchronous a.c. motor having a stationary winding with a series of pole pieces energized alternately in opposite magnetic directions by alternating current through said winding and having permanent magnetic poles on the rotor, without some provision for insuring the starting up of the motor armature in the right direction, has the inherent disadvantage that upon energization of the winding by alternating current the rotor may start rotating in either a forward direction or a backward direction, unless positive provision is made for preventing starting in the wrong direction, and for starting in the right direction.